Method and arrangement for locating areas having poor radio coverage

ABSTRACT

A method for determining tentative locations for areas with poor radio coverage in a cellular communication system comprises the step of keeping position-related data of connected user equipment&#39;s updated in a network part of the communications system. The method further comprises detection of an accidental loss of connection to a user equipment. The position-related data of such a dropped user equipment is logged as a response to a detection of such accidental loss of connection. The logged position-related data for a multitude of accidental loss events are compiled as a quantity based on the number of accidental losses of connection as a function of the position-related parameter. The method further comprises identification of a tentative location for an area with poor radio coverage by statistical evaluation of that quantity. An arrangement for determining tentative locations for areas with poor radio coverage is also presented.

TECHNICAL FIELD

The present invention relates in general to arrangements and methodsrelated to operation and maintenance of cellular communication systems,and in particular to arrangements and methods assisting in increasingradio coverage.

BACKGROUND

An important service quality issue in cellular communication systems isto provide complete and reliable radio coverage of the geographical areathat is intended to be covered by the cellular communication system.Cellular communication systems are typically optimized prior tocommercialization to give an as good radio coverage as possible.However, since surroundings within the coverage area may change withtime, coverage may also change. Adjustments of antennas, beams and/oremission powers are used to continuously minimize areas having poorradio coverage, typically on a network level. These efforts have beenquite successful and today, 3G networks (Third generation mobilenetworks) has reached and stabilized at a drop rate of around 0.7-1.0%.

Further improvements call for cell level trimming or re-planning, whichis more expensive and tedious. Such functionality is often referred toas O&M systems (Operation & Maintenance). A commonly adopted view-pointis that work aiming to decrease the drop rate even further requires avery large effort in relation to the potential improvements. Since thedrop rate is at a fairly low level today, further drop rate combattherefore has been considered as less important for the networkoperators, since such measures would lead to high costs.

A typical approach for further improving radio coverage is to visit theequipment sites and cell areas and actually measure the radio conditionsat different sites. However, since cells, at least in rural areas can bevery large indeed, in some cases even up to 10 000 km², it is naturallyvery time consuming and costly to cover such large areas manually whensearching for areas of poor coverage.

However, a continued call drop combat has clear advantages. The problemis that most prior art coverage tuning is based on a resource-demanding“blind” search for poor coverage areas.

In the published U.S. patent application US 2005/0136911, an apparatusand method for mobile station-assisted optimization of a wirelessnetwork are disclosed. Mobile stations are equipped with GPS receiversand are therefore continuously aware of their position. Radio signalparameters are stored in the mobile station and reported to a coverageserver in the core network together with corresponding positioninformation. In particular, when communication links to the wirelessnetwork are dropped, the mobile station reports the position for such adrop. The information is compiled in the coverage server and poorcoverage areas may be detected, as well as fault functioning mobilestations.

The solution of US 2005/0136911 gives at least theoretically a goodoverview of good and bad coverage areas. However, a number of severedrawbacks are present. The solution relies on the active action ofmobile stations, which calls for updated mobile stations. In particular,to reach the top resolution, GPS receivers have to be provided in themobile stations, which receivers increase the cost for each mobilestation tremendously. This makes it practically impossible to introducesuch equipment as standard equipment in mobile stations. Furthermore,the mobile station performs a large part of the processing, some of itoperating continuously, which increases the battery consumption. Thereporting of the position data and/or signal parameters requiresadditional radio transmissions, also leading to increased batteryconsumption. The radio transmissions also consume available resources inthe radio interface, leading to less traffic capacity. Furthermore,since mobile stations vendors are not typically allied with operators,there are small possibilities for the operators to influence the mobilestation vendors to provide suitable mobile stations. Since the radiointerface is standardized, the proposed solution needs substantialstandardization efforts. Moreover, the overall solution requires asubstantial and costly systemization and access network implementation.

A general problem with the solution of US 2005/0136911 is thus that thecoverage improvements are results entirely dependent of activeoperations performed mainly in the mobile stations.

SUMMARY

A general object of the present invention is to achieve informationassisting in locating tentative areas with poor radio coverage in acellular communication system without actively involving mobile stationsand/or the radio interface. A further object of the present invention isto achieve such information without any large needs for standardizationchanges or large systemization efforts.

The above objects are achieved by methods and arrangements according tothe enclosed patent claims. In general words, in a first aspect, amethod for determining tentative locations for areas with poor radiocoverage in a cellular communication system comprises the step ofkeeping position-related data of connected user equipments updated in anetwork part of the communications system. The method further comprisesdetection, in the network part of the communication system, of anaccidental loss of connection to a user equipment. The position-relateddata, available in the network part, of such dropped user equipment islogged as a response to a detection of such accidental loss ofconnection of the dropped user equipment. The logged position-relateddata for a multitude of accidental loss events are compiled as aquantity based on the number of accidental losses of connection as afunction of the position-related parameter. The method further comprisesidentification of a tentative location for an area with poor radiocoverage by statistical evaluation of that quantity.

According to a second aspect of the present invention, a network partarrangement for assisting in providing tentative locations for areaswith poor radio coverage in a cellular communication system comprisesmeans for keeping position-related data of connected user equipmentsupdated. The network part arrangement further comprises a detector ofaccidental loss of connection to a user equipment and means for loggingposition-related data. The means for logging position-related data isconnected to the means for keeping position-related data updated and thedetector. The means for logging position-related data is arranged forlogging the position-related data of a dropped user equipment as aresponse to a detected accidental loss of connection of the dropped userequipment.

According to a third aspect of the present invention, a cellularcommunication system node comprises an arrangement according to thesecond aspect.

According to a fourth aspect of the present invention, a cellularcommunication system comprises a node according to the third aspect.

An advantage with the present invention is that assisting informationabout tentative poor radio coverage locations are achieved by activeactions only within the network part of a cellular communication system.This facilitates implementation and does not have to rely on assistancefrom users or user equipment manufacturers/vendors.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with further objects and advantages thereof, maybest be understood by making reference to the following descriptiontaken together with the accompanying drawings, in which:

FIG. 1 is a block scheme of a general cellular communication system;

FIG. 2 is a block scheme of a WCDMA communication system;

FIG. 3 is a diagram showing a search window for propagation delays;

FIG. 4 illustrates the relation between propagation paths andpropagation delay;

FIG. 5 illustrates a flow diagram of steps of an embodiment of a methodaccording to the present invention;

FIG. 6 is a diagram illustrating a compilation of accidental loss ofconnection data;

FIG. 7A illustrates a cell having identified tentative areas for poorradio coverage;

FIG. 7B illustrates two cells having common identified areas for poorradio coverage;

FIG. 8 are diagrams illustrating normalizing of accidental loss ofconnection data;

FIG. 9 is a block scheme of an embodiment of a base station according tothe present invention;

FIG. 10 is a block scheme of an embodiment of an OSS node comprisingparts of an arrangement according to the present invention; and

FIG. 11 is a block diagram of an embodiment of a distributed arrangementaccording to the present invention.

DETAILED DESCRIPTION

Throughout the drawings, the same reference numbers are used for similaror corresponding elements.

FIG. 1 illustrates a block scheme of an embodiment of a general cellularcommunication system 100. Base stations 30 are spread over the coveragearea of the system and serves antennas 20, which in this embodiment aresectorized antennas. A cell 15 is associated with each sector of theantennas 20, as the area in which connection to the communicationssystem preferably is performed through that particular sector. The basestations 30 are connected to a control node 40. The control node 40 isfurther connected to a core network 50 of the communications system 100.The core network 50 in turn typically comprises a large number ofinterconnected nodes (not shown).

A user equipment (UE) 10 is situated in the area covered by the cellularcommunications system 100. In the present disclosure, the terms “mobileterminal”, “mobile station” and “user equipment” (UE) are used assynonyms. The UE communicates with the own base station 30 throughsignals 25. However, also signals 26 from and to neighbouring basstations 30 may be possible to detect. If the neighbouring signals 26are strong enough for supporting actual communication, the correspondingcell could be included in e.g. soft(er) handover.

The antennas 20, the base stations 30, the control node 40 and the corenetwork 50 are in the present disclosure defined as a network part 35 ofthe communication system 100. The base stations 30 and the control node40 as well as different nodes within the core network 50 are consideredas cellular communication system nodes. Some communication-related tasksare solved within a single node. An arrangement for such activitiestherefore comprises parts within one and the same node. However,different communication functionalities may also be the result ofcooperation between different nodes. An arrangement, e.g. a network partarrangement, may is such cases therefore comprise parts which arecomprised in different nodes.

The present invention is applicable to many different cellularcommunication systems. However, for illustrating purposes, aWCDMA-system will be used as an example system. Note that the use of theWCDMA system as an example is not intended for limiting the protectionscope thereto, and the protection scope should only be defined by theenclosed patent claims. The concept of the present invention can inprinciple be applied to any radio access technology, with possibility totrack the timing between a base station and a mobile terminal at thenetwork part of the system. Non-exclusive examples of possible usedstandards are GSM (global system for mobile communications), TDMA (Timedivision multiple access) (IS-136) and cdma2000 (IS-95) (CDMA=codedivision multiple access) or methods based on OFDM (Orthogonal FrequencyDivision Multiplexing) techniques.

FIG. 2 illustrates an architecture of a communication system 100, inthis example a WCDMA (Wideband Code Division Multiple Access)communication system 101. A UE 10 communicates over a radio interfacewith a base station (BS) 30, in the present example a node B 31. Thebase station 30 may be named differently in other systems, e.g. a radiobase station (RBS), or bas station transceiver (BST). One or severalnode B's 31 are connected to a control node 40, in this example a radionetwork controller (RNC) 41. The control node 40 may be nameddifferently in other systems, e.g. a base station controller (BSC). TheRNC 41 and the node B's 31 connected thereto constitutes a radio networksubsystem (RNS) 43. One or several RNS's 43 together constitutes anUTRAN (Universal mobile telecommunication system terrestrial radioaccess network) 42. The RNC's 41 communicates further with the corenetwork 50, and in particular to nodes, such as MSC/VLR (Mobile servicesswitching centre/visitor location register) nodes 52 or SGSN (Servinggeneral packet radio system support node) nodes 51. O&M functionalitiesare typically supported by an OSS (operations support system) node 53.

When a node B communicates with a UE, downlink signals are sent from thenode B to the UE and likewise, uplink signals are sent from the UE tothe node B. Radio propagation in the uplink as well as downlinkdirection is characterized by propagation time, multiple reflections,diffractions and attenuation. In order to be able to correctly interpretany received signals, a propagation delay has to be compensated for. Abaseband processor in the node B keeps track of propagation delays tothe different UE's connected to the node B. Each UE is associated with acertain synchronizing window, within which tracking is performed to findthe actual signal, see FIG. 3. Different methods and arrangements formultipath diversity reception are also typically available. The timeposition of the synchronizing window t0 is continuously updated, and thetime position of the strongest energy peak t1 relative the synchronizingwindow is known, which means that the uplink baseband processing givesupdated information of propagation delay to each UE. The synchronizationwindow and thereby the propagation is given in coding chips. In WCDMA,the chip duration at 3.84 Mcps is 0.26 μs.

As illustrated in FIG. 4, the propagation delay Δt has a directcorrespondence in distance d. Since radio signals travel with the speedof light, there is a direct correspondence between traveled time andtraveled distance. The baseband processor and therefore the base stationhave always updated position-related data to all UE's connected to thebase station. The traveled distance of the radio signal is in thetypical case the shortest distance between the UE and the base stationantenna. A resolution of 1 chip at 3.84 Mcps rate then corresponds to 78meters. In some cases, the situation may be more complex, if e.g.multipaths are possible. In FIG. 4, a radio signal may e.g. reflectagainst a building 99 and then arrive at the antenna. Another delay Δt′will then be detected for that signal. In most cases, the direct path isthe strongest one, and if detected always the first one. In other words,in a multipath situation, the smallest detectable propagation delayconstitutes a maximum limit for the true direct path delay. Theimportant conclusion is, however, that the base station always hasrecent position-related data concerning all UE's connected to the basestation.

The present invention presents a novel O&M statistics tool to pinpointspecific intra-cell problems areas. Every time a call drops, its lastknown “position” is logged by position-related data available in thenetwork part of the communication system. Call drops are in the presentdisclosure limited to an accidental loss of connection to a mobilestation as a result of radio failure. In particular such a radio failuremay be an uplink layer one synch loss or downlink layer tworetransmission time out. The “position” is the case of using thepropagation delay the physical distance between the MS and the servingradio base station antenna.

All position-related data are collected, e.g. in a PDF counter(probability density function) with highest possible resolution. For the3 GPP WCDMA standard a reasonable resolution is one single coding chip,corresponding to 78.125 meters. Possibly, a resolution of ½ chip may beavailable in special situations. When sufficient statistical data hasbeen collected, one can easily detect if there are any “positions” withabnormally high drop concentration. The detection can be manual orautomized. The precision of the locator is likely to be a circular stripwith a width of less than 200 meters. The positioning can also beimproved (circumferentially) by means of thinner antenna beams. This canbe accomplished either by (higher) sectorization or electronical beamforming. For example, changing from a 3-sector site to a 6-sector meansthe nominal beam angle goes from 120 degrees to 60 degrees. Beam forminghas yet an advantage in that it can be performed in real time or as aremotely controlled procedure.

The benefit from such a locator is obvious. Instead of having to searchthrough an entire cell area for locating poor coverage spots, such asearch can be limited to a 200 m wide strip. For a large cell of aradius of 200 km, the tentative “location” for poor radio coverage islimited to 0.1% of the entire cell area.

FIG. 5 is a flow diagram illustrating an embodiment of a methodaccording to the present invention. A method for determining tentativelocations for areas with poor radio coverage in a cellular communicationsystem starts in step 200. In step 210, position-related data ofconnected user equipments is kept updated in a network part of thecommunications system. Preferably, the position-related data is adistance-related quantity, and more preferably such a distance-relatedquantity is a propagation delay. An accidental loss of connection to auser equipment is detected in the network part of the communicationsystem in step 212. In step 214, position-related data, available in thenetwork part, of a dropped user equipment is logged as a response tosuch a detected accidental loss of connection of the dropped userequipment. Preferably, the logged position-related data isposition-related data of a latest known position of the user equipment.The steps 210 to 214 are typically performed continuously orintermittently a number of times, as indicated by the arrow 215. Thelogged position-related data for a multitude of accidental loss eventsis compiled in step 216 as a quantity based on the number of accidentallosses of connection as a function of a position-related parameter. Thisposition-related parameter is typically directly derivable from theposition-related data. In step 218, a tentative location for an areawith poor radio coverage is identified by statistical evaluation of thecompiled quantity. The procedure ends in step 299.

This way the network operations can use the regular subscriber trafficvolume to find locations with poor radio coverage. Instead of havingexpensive drive test teams blindly searching for bad coverage spots,they can now limit the surveys to pinpointed areas. Furthermore, theutilization of the subscriber traffic does not influence thesimultaneous performance of the UE's, e.g. in terms of increased powerconsumption, need for additional hardware or increased controlsignaling. An intra-cell problem area can now be narrowed down to acircular strip with typically a width of approximately 200 meters aroundthe node B site. By this approach, it may be worth the efforts to chasethat typical last percent of the network drop rate. The identificationof the poor coverage area of the present invention is typically in mostcases not precise enough to point out a specific spot, but the locationindication is good enough to limit the area which has to be search forfinding the actual poor coverage spot.

The compiling step is important, since it enables a distinction betweenaccidental losses that are dependent on poor radio coverage fromaccidental losses being caused by other reasons. Such other reasonscould be malfunctions of the UE's, e.g. loss of battery power.Accidental losses caused by “other reasons” are typically not directlydependent on the location of the UE. By collecting a certain statisticalbasis, non-location dependent causes for accidental loss of connectionwill appear as a background or smeared-out distribution. Thelocation-dependent accidental loss of connections will instead sum up todistinct peaks in the statistical ensemble.

The most straight-forward way of compiling the drop data is to selectthe actual number of accidental losses of connection as the quantity tobe mapped as a function of a position-related parameter. FIG. 6illustrates such a plot, where the number of detected accidental lossesof connection is illustrated as a function of a position-relatedparameter, in this embodiment the propagation delay. Peaks are buildingup at propagation delays, where poor radio coverage is present. A simplemethod for identification of such propagation delays is to identifypositions with a value of the plotted quantity, i.e. in this embodimentthe number of accidental losses of connection, as a function of theposition-related parameter, i.e. in this embodiment the propagationdelay, over a predetermined threshold T as a tentative location for anarea with poor radio coverage. In FIG. 6, two peaks P1 and P2 arepossible to identify. Each peak corresponds to a circular arc sectorcentered around the base station site with a radius determined by thepropagation delay times the speed of light.

FIG. 7A illustrates a cell corresponding to the example of FIG. 6. Afirst area A1, being a circular arc sector with a radius R1corresponding to the propagation delay of P1 (FIG. 6) can be identifiedas a tentative location of a poor coverage area. If no furtherinformation is available, the entire circular arc sector A1 has to besearch for finding the actual poor coverage spot. In the case of P2(FIG. 6), another radius R2 is associated. In the cell 15 of FIG. 7A, alake 98 is present, and the circular arc sector of radius R2 intersectsthe lake 98. In this example, it may be very unlikely that any UE's, orat least a large number of UE's have been used at the lake area. Thearea to be searched for the poor coverage spot can thereby by use ofadditional local information be limited to two part areas A2 and A3.

In cellular communication systems, there is typically a certain degreeof overlap between different neighbouring base stations. This enablese.g. handover between different node B's. This means that in some cases,there might be accidental loss of connection data for one and the samespot available from more than one base station. FIG. 7B illustrates asituation, where two circular arc sectors A4, A5 centred at differentnode B sites intersect. Since each of those node B sites pinpoints apoor coverage ring and the rings geographically overlap when theirlayouts are combined, then the precision of the tentative poor coveragelocation may increase to a spot S of typically 200×200 meters. Combiningof data from several node B's may easily be performed in an automaticfashion on a centrally located network node.

The statistical evaluation directly on the number of accidental loss ofconnection can be even improved if further considerations are taken intoaccount. The area corresponding to a certain propagation delay is largerfor large propagation delays than for small propagation delays, sincethe length of the circle arcs increases. This means that there aregenerally more UE's available at the same propagation delay when thepropagation delay is large. This will then also give a higher rate ofaccidental losses of connection being caused by other causes than poorradio coverage, and might eventually give a statistical peak that mightbe identified as a problem area. If the compilation therefore isnormalized by a division of a quantity proportional to the propagationdelay itself, a more correct statistics will result. However, attentionshould be taken to treat the area closest to the node B site carefully,since each drop will gain a very high weight in the statisticalcompiling.

Another situation which may influence the evaluation of the compileddata is if the traffic load differs considerably between different areaswithin the cell. For instance, places where a lot of people pass, suchas shopping malls, sports arenas or transport nodes, will typicallyexhibit a higher rate of calls than other areas in the cell. Sinceaccidental losses of connection not dependent on the location typicallyare proportional to the total number of calls, more accidental losses ofconnection are expected to appear in high-traffic areas. By normalizingthe number of accidental loss of connection by a quantity representingthe total traffic load, a more representative value can be found. Thetraffic load quantity can be of any type, e.g. an average trafficrecorded during a test period.

One quantity that may be used as a representation of a “total trafficload” measure is the number of new connections per area. An area havinga high traffic load is also expected to have a high number of newconnections. This quantity has probably also some information concerningpossible poor coverage, since it is unlikely that new connections areestablished in areas where the coverage is poor. Furthermore, uponinitializing a new connection, the propagation delay and hence thedistance to the node B is always determined. The logging step of thepresent invention therefore preferably also comprises logging of userequipment connection positions when the user equipment being connectedto the cellular communication system and the compiling further comprisescompiling of the user equipment connection positions as a function of aposition-related parameter. By dividing the number of accidental lossesof connection with the number of new connection as a function of e.g.propagation delay, i.e. a normalizing operation, areas having a hightraffic load are suppressed compared to areas having lower traffic load.Areas having extremely low traffic load due to poor coverage will haveboth a high drop rate and a low rate of new connections, which willpronounce the peaks even more. In order to avoid division be very smallnumbers, the normalization is preferably performed by a measure based onan average of the user equipment connection positions as a function of aposition-related parameter over a predetermined area surrounding theposition defined by the position-related parameter. In other words, thenormalizing factor is averaged over a larger area than the accidentalloss of connection quantity.

FIG. 8 presents diagrams schematically illustrating such normalizing. Acurve 110 corresponds to an un-normalized distribution of call drops(i.e. accidental loss of connection), curve 111 corresponds to adistribution of new connections and curve 112 corresponds to anormalized distribution of call drops.

As mentioned above, the functionality of the present invention may beimplemented in many different ways in different network part nodes. Afew examples of node implementations are presented below.

FIG. 9 is a block scheme of an embodiment of a base station 30 having anarrangement 60 for assisting in providing tentative locations for areaswith poor radio coverage in a cellular communication system. Note thatthis arrangement 60 is entirely comprised in the network part of thecellular communication system. The arrangement 60 comprises an uplinkbase band processor 32. The uplink base band processor 32 is furtherarranged for keeping position-related data of connected user equipmentsupdated, preferably a distance-related quantity. A means 36 for keepingposition-related data of connected user equipments updated can thus beseen to be integrated within the uplink base band processor 32. Theupdating is typically provided by tracking a propagation delay for theuser equipments, and particular for tracking a representation of acoding chip of the propagation delay.

The arrangement 60 further comprises a detector 37 of accidental loss ofconnection to a user equipment. This detector is typically integratedwith other processors in the base station 30. A means 33 for loggingposition-related data, typically a data storage, is connected to themeans 36 for keeping position-related data updated and to the detector37. The means 33 for logging position-related data is arranged forlogging the position-related data of a dropped user equipment as aresponse to a detected accidental loss of connection of the dropped userequipment. The position-related data is preferably position-related dataof a latest known position of said user equipment.

The means 33 for logging position-related data is preferably alsoarranged for logging connecting user equipment positions when theconnecting user equipment is connected to he cellular communicationsystem. This data can, as discussed above, be used for normalizingpurposes.

Typically, further processing of the logged data is performed in anothernetwork part node of the cellular communication system. The presentembodiment of the network part arrangement 60 therefore comprises atransmitter 34 for transmitting data representing the loggedposition-related data to the node within the cellular communicationsystem having appropriate further processing or storing capacity.

A network part node that is utilized for many O&M related tasks is theOSS node. Parts of an arrangement assisting in providing tentativelocations for areas with poor radio coverage are with advantage providedan OSS node. FIG. 10 illustrates a block scheme of an embodiment of anOSS node 53 exhibiting parts of an arrangement 60 assisting in providingtentative locations for areas with poor radio coverage. The OSS node 53comprises a receiver 54 for data representing the loggedposition-related data. Such data is preferable intermittentlytransmitted from e.g. the base station are regular occasions, e.g. asparts of regular O&M related control signaling, and is preferably storedin a data storage 55 of the OSS 53. In case of WCDMA, such signaling ispreferably performed over Mub/Mu interfaces, shown further below inconnection with FIG. 11. When appropriate amounts of data are stored, acompilation takes place. The OSS 53 therefore comprises a compiler 56for compiling the logged position-related data for a multitude ofaccidental loss events as a quantity based on the number of accidentallosses of connection as a function of a position-related parameter. Thequantity is in one embodiment the actual number of accidental losses ofconnection as a function of said position-related parameter. Thecompiler 56 is in one embodiment further arranged for also compilingconnecting user equipment positions as a function of a position-relatedparameter. The compiler 56 can thereby normalize the actual number ofaccidental losses of connection as a function of said position-relatedparameter by a measure based on the connecting user equipment positions,preferably averaged over a predetermined area surrounding the positiondefined by the position-related parameter.

The results from the compiler 56 may be evaluated manually. However, inthe present embodiment, the OSS node 53 also comprises an evaluator 57for identifying a tentative location for an area with poor radiocoverage. The evaluator 57 is connected to the compiler 56 and arrangedfor statistical evaluation of the compiled quantity based on the numberof accidental losses of connection as a function of the position-relatedparameter. Such evaluation is preferably performed according to theprocedures discussed further above.

In case the arrangement for assisting in providing tentative locationsfor areas with poor radio coverage only comprises the means connected tothe updating of position-related data and logging of droppedconnections, the arrangement may easily be comprised in a single networkpart node, e.g. a base station, a base station controller, a node B or aradio network controller. However, if the arrangement also comprisescompilation and evaluation means, it is typically advantageous that suchfunctionality is provided higher up in the network hierarchy. Thearrangement for assisting in providing tentative locations for areaswith poor radio coverage then becomes a distributed arrangementinvolving parts of different cellular communication system nodes. FIG.11 illustrates such a system. In the illustrated embodiment, thearrangement 60 involves parts of both the node B 31 and the OSS node 53.The intermediate nodes, e.g. the RNC 41 and the MSC/VLR 52 may be puretransit nodes which the information simply passes without causing anyoperations. The RNC 41 and the Node B 31 communicates over the logicalO&M interface Mub 58 and the RNC 41 communicates with the core network,here illustrated by e.g. the MSC over the logical O&M interface Mu 59.However, the intermediate nodes may also be used e.g. as intermediatestorages for information. In such a way, the RNC 41 or the MSC/VLR 52can collect data from several connected node B's for a certain period oftime, and when an evaluation is to be performed, e.g. in the OSS node,the data could be retrieved and sent to the OSS node 53 for compilationand evaluation. In alternative embodiments, the RNC 41 and/or theMSC/VLR 52 may also comprise parts of the arrangement 60.

The RNC 41 may in some situations be utilized for improving the qualityof the positioning of tentative locations of poor coverage. In mostcases, accidental drops occur in situations with only one remainingradio link, i.e. only one node B involved. In systems having softhandover, a terminal may, however, be in simultaneous contact with morethan one node B. In such a case, there is a certain uncertainty aboutthe round trip time measured e.g. by the BB UL processing. The positiondetermination may therefore be very inaccurate. Such situations may,however, easily be excluded by assistance from the RNC. The RNC has toreport to the node B that it changes from single link to multiple links.In the 3 GPP Iub Frame Protocol specification, there is an entity in aheader that can be used for such “multiple-RLS indicator” purposes. RLSmeans Radio Link Set, which is the notation for all radio links withinone node B. If the indicator is activated, another node B issimultaneously involved in the connection of the mobile terminal.

Another alternative is to involve the soft handover situation, which canbe accomplished if the logging at least to a part is moved to the RNC. Ameasurement from the mobile terminal is demanded periodically in orderto compensate the data before logging for the statistical evaluation.Dedicated signals over NBAP and RRC have to be employed. A RRCmeasurement control message is first sent to the terminal requesting areception-to-transmission time measurement. Then, a NBAP dedicatedmeasurement control message is sent to the node B to request an RTTmeasurement. The terminal will respond with a RRC measurement reportmessage and the node B with a NBAP dedicated measurement report message.When the RNC has received both measurement reports, the distance valuefor the terminal can be calculated as half the difference between theround trip time and the reception-to-transmission time.

The embodiments described above are to be understood as a fewillustrative examples of the present invention. It will be understood bythose skilled in the art that various modifications, combinations andchanges may be made to the embodiments without departing from the scopeof the present invention. In particular, different part solutions in thedifferent embodiments can be combined in other configurations, wheretechnically possible. The scope of the present invention is, however,defined by the appended claims.

REFERENCES

Published U.S. patent application 2005/0136911.

1. Method for determining tentative locations for areas with poor radiocoverage in a cellular communication system, comprising the steps of:keeping position-related data of connected user equipments updated in anetwork part of said communications system; detecting, in said networkpart of said communication system, an accidental loss of connection to auser equipment; logging said position-related data, available in saidnetwork part, of a dropped user equipment as a response to a detectedsaid accidental loss of connection of said dropped user equipment;compiling said logged position-related data for a multitude ofaccidental loss events as a quantity based on the number of accidentallosses of connection as a function of said position-related parameter;and identifying a tentative location (A1; A2; A3; S) for an area withpoor radio coverage by statistical evaluation of said quantity.
 2. TheMethod according to claim 1, wherein said position-related data of alatest known position of said user equipment.
 3. The Method according toclaim 1, wherein said quantity is the actual number of accidental lossesof connection as a function of a position-related parameter.
 4. TheMethod according to claim 1, wherein said position-related data is adistance-related quantity.
 5. The Method according to claim 4, whereinsaid distance-related quantity is a propagation delay.
 6. The Methodaccording to claim 5, wherein said propagation delay is achieved byuplink baseband processing.
 7. The Method according to claim 5, whereinsaid position-related parameter is a representation of the coding chipof said propagation delay.
 8. The Method according to claim 1, whereinsaid step of identifying identifies positions with a value of saidquantity based on the number of accidental losses of connection as afunction of a position-related parameter over a predetermined thresholdas tentative location (A1; A2; A3; S) for an area with poor radiocoverage.
 9. The Method according to claim 1, wherein said step oflogging further comprises logging of user equipment connection positionswhen the user equipment being connected to said cellular communicationsystem and said step of compiling further comprises compiling of saiduser equipment connection positions as a function of a position-relatedparameter.
 10. The Method according to claim 9, wherein said normalizedquantity based on the number of accidental losses of connection as afunction of a position-related parameter is normalized by a measurebased on said user equipment connection positions as a function of aposition-related parameter.
 11. The Method according to claim 10,wherein said normalized quantity based on the number of accidentallosses of connection as a function of a position-related parameter isnormalized by a measure based on an average of said user equipmentconnection positions as a function of a position-related parameter overa predetermined area surrounding the position defined by saidposition-related parameter.
 12. The Method according to claim 1, whereinsaid step of identifying utilizes compiling logged position-related datafrom more than one base station for limiting an area of said tentativelocation (S) for an area with poor radio coverage.
 13. A Network partarrangement for assisting in providing tentative locations (A1; A2; A3;S) for areas with poor radio coverage in a cellular communicationsystem, comprising: means for keeping position-related data of connecteduser equipments updated; detector of accidental loss of connection to auser equipment; means for logging position-related data, connected tosaid means for keeping position-related data updated and said detector;said means for logging position-related data logging saidposition-related data of a dropped user equipment as a response to adetected said accidental loss of connection of said dropped userequipment; and means for compiling said logged position-related data fora multitude of accidental loss events as a normalized quantity based onthe number of accidental losses of connection as a function of aposition-related parameter.
 14. The Network part arrangement accordingto claim 13, wherein said position-related data is position-related dataof a latest known position of said user equipment.
 15. The Network partarrangement according to claim 13, wherein said position-related data isa distance-related quantity.
 16. The Network part arrangement accordingto claim 15, wherein said means for keeping position-related data is anuplink baseband processor.
 17. The Network part arrangement according toclaim 16, wherein said uplink baseband processor tracks a propagationdelay as said position-related data.
 18. The Network part arrangementaccording to claim 17, wherein said uplink baseband processor tracks arepresentation of a coding chip of said propagation delay as saidposition-related data.
 19. The Network part arrangement according toclaim 13, wherein means for logging position-related data logsconnecting user equipment positions when said connecting user equipmentbeing connected to said cellular communication system.
 20. The Networkpart arrangement according to claim 13, further comprising means fortransmitting data representing said logged position-related data to anode within said cellular communication system.
 21. The Network partarrangement according to claim 13 wherein said quantity is the actualnumber of accidental losses of connection as a function of saidposition-related parameter.
 22. The Network part arrangement accordingto claim 13, wherein said means for compiling compiles connecting userequipment positions as a function of a position-related parameter. 23.The Network part arrangement according to claim 22, wherein said meansfor compiling normalizes said quantity by a measure based on saidconnecting user equipment positions.
 24. The Network part arrangementaccording to claim 23, wherein said normalizing is based on an averageof said connecting user equipment positions as a function of aposition-related parameter over a predetermined area surrounding theposition defined by said position-related parameter.
 25. The Networkpart arrangement according to claim 13, further comprising an evaluatorfor identifying a tentative location (A1; A2; A3; S) for an area withpoor radio coverage to statistically evaluate said quantity based on thenumber of accidental losses of connection as a function of saidposition-related parameter.
 26. The Network part arrangement accordingto claim 13, further comprising means for receiving data representingsaid position-related data from a node within said cellularcommunication system.
 27. The network part arrangement according toclaim 13, wherein a Cellular communication system node comprises saidnetwork part arrangement.
 28. The Cellular communication system nodeaccording to claim 27, being one of: a node B; a radio networkcontroller; an operations support system node; a base station; a basestation controller; and a mobile switching centre.
 29. The cellularcommunication node of claim 27 wherein a Cellular communication system,comprises at least one cellular communication node.
 30. The Cellularcommunication system according to claim 29, being one of: a WCDMAsystem; a GSM system; a CDMA system; a TDMA system; and an OFDM system.